docs: post-merge consistency sweep with new recipes

[catgoose]

Summary

• Spot-checked all docs for stale control-event descriptions -- existing docs (README, stream-contract.md, delivery-observability.md, snapshot-replay.md) were already consistent with structured JSON payloads
• Added SubscriberTopics() API mention to README subscriber management section
• Trimmed README "App-shell lifeline architecture" section to a brief summary + links to docs/stream-contract.md, Recipe 27, and Recipe 31 (was duplicating the full contract)
• Added 4 new recipes to RECIPES.md:
  • Recipe 29: Interaction insulation for hot-region commands -- Go handler + tavern-js delegated commands with tavern-command-delegate/tavern-command-target
  • Recipe 30: Consuming structured control events in app code -- tavern-js DOM events + raw SSE EventSource listeners for all control event payloads
  • Recipe 31: App-shell with lifeline and scoped streams -- complete app-shell with lifeline handler, navigation handler, scoped panel, AddTopic/RemoveTopic, and client-side tavern:topics-changed handling
  • Recipe 32: Stale/degraded/live region handling -- full state machine, HTML with tavern-stale-class/tavern-live-class, CSS, Go server config, and programmatic hooks

Test plan

• go test ./... passes
• Verify doc links resolve correctly
• Review recipe code examples for accuracy

Closes #218